The present invention relates generally to a control apparatus for a vehicle, and more particularly to a vehicle control apparatus in which testing of the control apparatus can be carried out in a short time.
Conventionally, there has generally been used an engine control apparatus in which the oxygen concentration in the exhaust gas is detected by an O.sub.2 sensor mounted in the exhaust pipe. After the engine is warmed up, the output of the sensor is used to feedback-control the fuel supply rate so as to hold the air-fuel ratio at the theoretical value (.lambda.=1). Such feedback control is not used, however, until the engine has been warmed up. Prior to the engine being warmed up, the fuel supply rate is held at a fixed, predetermined value. Such a system is disclosed, for example, in Japanese Unexamined Patent Publication No. 117828/1979.
Air-fuel feedback control using the O.sub.2 sensor is also not performed in cases other, for example, during starting, deceleration, and running under high-load conditions.
Referring now to FIGS. 1 and 2, a description will be provided of a general example of a conventional vehicle control apparatus. FIG. 1 is a block diagram showing the overall arrangement of an air-fuel ratio control system. In this drawing, the air-fuel ratio control system is constituted by a control apparatus 1, a sensor power source line 21, a throttle opening sensor 22 constituted by a variable resistor for converting the throttle opening into a voltage signal, a coolant temperature sensor 23 using a thermistor, and a sensor ground line 24.
The sensor power source line 21, the throttle opening sensor 22, and the sensor ground line 24 are connected in series with each other between terminals 141 and 144, and a movable terminal of the throttle opening sensor 22 is connected to a terminal 142. The coolant temperature sensor 23 is connected to a terminal 143.
An O.sub.2 sensor 25, an ignition coil 26, and an idling switch 28 are connected to terminals 145, 146, and 147, respectively.
The O.sub.2 sensor 25 detects the oxygen concentration in the exhaust gas. An igniter 27 is provided for controlling the ignition coil 26. The ignition coil 26 and igniter 27 are connected in series with each other between a power source and ground. The idling switch 28 detects the state where the throttle is not depressed.
A power source circuit 109 is provided for supplying power to the throttle opening sensor 22 and various other portions of the control apparatus 1, the output terminals of the power source circuit 109 being connected to ground through a series connection of resistors 106 and 107. The resistors 106 and 107 constitute a resistor network together with the coolant temperature sensor 23 used to convert the coolant temperature to a voltage signal.
The terminals 142, 143, 145, 146 and 147 are connected to the input terminals of input interface circuits 101, 108, 103, 104, and 105 (hereinafter simply referred to as input I/Fs), respectively. The input I/F 108 constitutes an input I/F 102 together with resistors 106 and 107. Each of the input I/Fs 101 through 105 and 108 is constituted by a filter circuit for eliminating noise components, etc.
The outputs of the input I/Fs 101, 108, and 103 are applied to an A/D (analog-to-digital) converter 110, while the outputs of the input I/Fs 104 and 105 are applied to a microcomputer 120.
The A/D converter 110 converts the analog voltage signals produced by the input I/Fs 101, 103 and 108 into digital signals, which are transferred to the microcomputer 120.
The microcomputer 120 is provided with a RAM (random access memory) 121 and a ROM (read-only memory) 122. Output signals of the microcomputer 120 are amplified by output interface circuits 131, 132 and 134 (hereinafter simply referred to as output I/Fs), and applied to a fuel control solenoid 301 and other solenoids 302 and 303 through terminals 151 through 153, respectively.
The fuel control solenoid 301, incorporated in a carburetor, controls the air-fuel ratio on the basis of the controlled value of its duty cycle. The solenoids 301 and 303 control the exhaust gas flow.
Next, the operation of the control apparatus 1 of FIG. 1 will be described. The microcomputer 120 is supplied with digital signals obtained by digitally converting the respective outputs of the throttle opening sensor 22, the coolant temperature sensor 23, and the O.sub.2 sensor 25 by the A/D converter 110 so as to thus read input information from the sensors 22, 23 and 25.
The microcomputer 120 is supplied with an interrupt signal for the ignition coil 26 through the terminal 146 and the input I/F 104 to thereby permit it to measure the ignition timing interval and to convert the ignition timing interval into a value indicative of engine rotation speed, which is utilized for various control purposes.
Further, the microcomputer 120 judges the ON/OFF state of the idling switch 28 on the basis of an input voltage.
The states of the control signals for the fuel control solenoid 301 and the solenoids 301 and 303 are determined by the microcomputer 120 on the basis of the foregoing input information and in accordance with a procedure stored in the ROM 122. The solenoids 302 and 303 are turned off when the engine speed exceeds a predetermined value.
The fuel control solenoid 301, on the other hand, is controlled on the basis of the flowchart of FIG. 2. Referring to FIG. 2, in step 401, when the engine speed is not larger than 400 r.p.m., it is judged that the engine is being cranked for starting. When the engine is in this state, a predetermined controlled duty-cycle value for starting is produced as a control quantity in step 402.
In the microcomputer 120, the duty-cycle value is converted into a pulse signal using a well-known timer interrupt procedure so as to control the duty-cycle of the fuel control solenoid 301.
Similar to the above case, when the duty-cycle value for controlling the fuel control solenoid 301 is set, the duty-cycle value is converted into a pulse signal by the timer interrupt processing.
The state of engine deceleration is detected from the engine speed and the output of the idling switch 28 in the step 403, and if the engine is decelerating, a control duty-cycle value for deceleration is set as the control quantity for the deceleration state in step 404. On the basis of the engine speed and the output of the throttle opening sensor 22, a judgment is made as to whether the engine is operating in the enriched zone (high-load running conditions) in step 405, and if so, a control duty-cycle value appropriate for the enriched zone is set in step 406.
The fact that the engine is running cold, that is, that the temperature of the coolant is low, is detected on the basis of the output of the coolant temperature sensor 23 in step 407, and if a low coolant temperature is detected, a suitable predetermined control duty-cycle value is set in step 408.
Judgment is made as to whether a time T.sub.1 (sec) has elapsed after starting of the engine in step 409, and if T.sub.1 has not elapsed after engine starting, a predetermined control duty-cycle value for this initial running period is set in step 410.
When the operation shifts from step 409 to step 411, normal air-fuel ratio feedback control by the O.sub.2 sensor 25 is performed to thereby determine the control duty-cycle value using the well-known technique of proportional integral control so as to hold the air-fuel ratio at the theoretical value.
To test the control apparatus 1 described above as an independent unit, a signal is applied to the input terminal of the control apparatus 1 and the resulting output signal produced upon the output terminals of the control apparatus 1 is detected. Thus, it is generally possible to confirm that the control apparatus 1 has correctly processed the input signal and correctly controlled the fuel control solenoid 301 and the solenoids 301 and 303. (The solenoids 302 and 303 can be turned on/off by changing the engine speed.)
Further, in steps 401 through 408 discussed above, it is possible to confirm that the input information, except for that provided by the O.sub.2 sensor 25, has been correctly read by applying simulated signals for those sensors to the terminals 141 through 147, thereby making it possible to test whether or not the control apparatus 1 is correctly operating within a short period of time. The operation of the fuel control solenoid 301 can also be confirmed in this manner.
In order to test the control operation of the O.sub.2 sensor 25, however, it is necessary that step 411 above be reached. That is, in order to confirm the operation of the O.sub.2 sensor 25 and to confirm the fact that the output of the O.sub.2 sensor 25 has been correctly read, in step 411, it is necessary that time T.sub.1 has elapsed after starting (step 409).
However, for mass production, it is necessary to shorten the unit test time for each product. In the case of the foregoing control apparatus, however, the test time is increased by T.sub.1, and therefore there has been a problem in that the mass-production of such control apparatus is lengthened, and consequently the cost increased.